1. Field of the Invention
The present invention relates to a ball chair, and more particularly to a ball chair having multiple strengthening blocks at joints of the ball chair to avoid the ball chair from cracking at the joints.
2. Description of the Related Art
A conventional ball chair is composed of a chair and a ball-shaped cushion. With reference to FIGS. 5 and 6, the conventional chair has a seat (50), at least three legs (52), at least three wheels (53), a backrest (54), two arms (56), a ball cushion (60) and a positioning element (70). The seat (50) has with a top face (51), a bottom surface, a side edge, a recess (500) and a passage. The recess (500) is defined in the top surface of the seat (50) near the side edge. The passage is defined in the top face (51) of the seat (50) to receive the ball cushion (60). The legs (52) are attached to the bottom face of the seat (50) to support the ball chair. The wheels (53) are respectively attached to the legs (52). The backrest (54) has an inserted end (542) and presses the ball cushion (60), and the inserted end (542) is mounted inside the recess (500) in the seat (50). The arms (56) are mounted on the side edge of the seat plate (50) and opposite to each other for holding the ball cushion (60) in position. The positioning element (70) is mounted on the arms (56) for holding the ball cushion (60) in position.
When a user sits on the ball chair, the ball cushion (60) is pressed to deform forward. The user is only supported by the backrest (54) inserted into the recess (500), the seat (50) is broken easily at the sidewall of the recess (500) and the backrest (54) is broken easily. Further, the inserted end (542) of the backrest (54) must completely be inserted into the recess (500) in the seat (50), or a poor quality ball chair will be made. Therefore, the backrest (54) cannot provide an enough supporting effect to a user, the conventional ball chair is not safe and stable in use.
The present invention has arisen to mitigate or obviate the disadvantages of the conventional ball chair.